1. Field of the Invention
The present invention relates to an aqueous dispersion for electrodeposition, a high dielectric constant film formed from the aqueous dispersion and electronic parts provided with the high dielectric constant film.
2. Description of the Prior Art
A technique is known whereby a high dielectric constant layer is formed on a multilayer printed wiring board or the like and the layer is utilized as a condenser. The high dielectric constant layer is fabricated, for example, by a method in which a solution of a thermosetting resin in an organic solvent also containing an added high dielectric constant inorganic powder is impregnated into a fiber-reinforcement such as glass fibers to compensate for the fragility of the thermosetting resin, and the solvent is then scattered and allowed to harden.
Because this prior art method uses a fiber-reinforcement it is not possible to achieve significant reduction in the thickness of the high dielectric constant layer (for example, to under 50 μm), and since the dielectric constant of a fiber-reinforcement is lower than that of an inorganic powder such as TiO2, it has not been possible to obtain condensers with high capacitance.
In order to solve this problem, Japanese Laid-open Patent Publication No. 12742 of 1997 discloses a high dielectric constant film that eliminates the need for the fiber-reinforcement in the aforementioned construction by using a thermosetting resin with film forming properties. According to this publication, a resin varnish is prepared containing the thermosetting resin and high dielectric constant inorganic powder, and this is coated and dried to produce a film.
However, since high dielectric constant inorganic powders usually have a high specific gravity and thus settle in resin varnishes with time, causing a lack of shelf life for such resin varnishes, it has been necessary to prepare a fresh resin varnish just before production of the film. Because the film is formed by coating and drying the solution, it is difficult to achieve a high film thickness precision for the obtained film, and the manageability has not been very good for formation of films on only specific locations of boards.
In addition, when forming a high dielectric constant layer selectively on a desired wiring, it has been necessary to prescribe the location of formation by a combination of photolithography and printing methods for conventional resin varnishes. However, formation methods using photolithography are associated with problems of high cost and complicated steps, while printing methods are associated with the problem of poor working precision.